Metallic pipelines are commonly used to transport oil, gas, and many other liquids. As soon as a pipeline is buried, corrosion, which is a natural electrochemical process, commences at locations on the pipe which are not covered by a protective coating. It is a common practice to apply cathodic protection, a technique to prevent the corrosion of a metal surface by making that surface the cathode of an electrochemical cell, to prevent or decrease the corrosion of buried pipelines at defects and anomalies in the pipeline coating.
Casings are commonly used to surround and protect pipelines where the pipelines cross beneath roadways, railroads, and bodies of water such as streams, rivers, and canals. Contact of a bare casing pipe with the pipeline usually results in a substantial lowering of the pipeline electrical potential and an accompanying loss of cathodic protection. Thus measures are taken during construction of the buried pipeline crossing to prevent any contact between the metal casing and the metal pipeline. Nevertheless, an electrical "short" may occur caused by water in the casing, allowing current to flow through the water and on to the pipeline within the casing.
The U.S. Department of Transportation has regulatory authority over interstate pipelines. Their regulations require that all highway and railroad crossings involving cathodically protected pipelines must be electrically isolated from the casing, or other measures must be used to mitigate or monitor galvanic corrosion of the pipeline inside the shorted casing. Once a "shorted casing" is found, measures must be taken to correct or negate the adverse effects of the shorted casing, including either clearing the short, if practical, or filling the casing/pipeline interstitial space with a high dielectric casing filler or other material which provides a corrosion inhibiting environment.
Various materials have been used as casing fillers. They are generally of two types, either "hot fill" or "cold fill". The "hot fill" type, represented by various petroleum waxes and petrolatums, are applied hot such that the material is above its melting point. After being pumped into the casing/pipeline interstitial space, it cools and hardens in place. The "cold fill" type of casing filler is applied by pumping a viscous material at ambient temperatures into the casing/pipeline interstitial space. This type of filler is typically a gelled or viscosified petroleum oil having a grease-like consistency.
Cushing U.S. Pat. No. 3,774,403 discloses the use of a polymeric electrically nonconductive material, such as polyurethane foam, as a casing filler. Kennedy, Jr. U.S. Pat. No. 4,469,469, incorporated herein by reference, discloses the typical means by which a casing filler is applied to the interstitial space between the pipeline and casing.